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KEY POINTS

Most common chromosomal abnormality that occurs in females. Only 1%of conceptuses with Turner syndrome survive to term.

Incidence is 1 in 2500 female livebirths. No association with advanced maternal age.

Approximately 50% of cases have full 45, X, 30% to 40% have mosaicism, and 10% to 20% have a structural abnormality of one X chromosome. Severity of clinical phenotype cannot be predicted from the karyotype.

Characteristic sonographic abnormalities include very large cystic hygroma, hydrops fetalis, short femur, coarctation of the aorta, hypoplastic left heart, and renal anomalies.

In the presence of lymphatic or cardiac malformations, delivery should occur at a tertiary center.

Major considerations for long-term follow-up include: growth hormone treatment for short stature, estrogen treatment for feminization and bone health, monitoring for cardiovascular complications such as aortic dilatation and rupture, severe hypertension, and propensity toward autoimmune disease.

Intelligence is normal, but there may be mild learning difficulties related to visual-spatial issues.

Phenotype may differ depending upon whether the maternal or paternal X is retained. In ~75% of women the maternal X remains.

CONDITION

Turner syndrome is named for Henry Turner, who in 1938 recognized the combination of sexual infantilism, webbed neck, and cubitus valgus to be a distinct entity. However, the underlying chromosomal abnormality in the condition was not recognized until 1959 (Ford et al., 1959). Turner syndrome exclusively affects females, and affected patients are generally missing all or part of the X chromosome in all or part of their cells. Postnatally, Turner syndrome is clinically suspected because of short stature, gonadal dysgenesis, or lymphedema. There are no pathognomonic clinical features (Hall and Gilchrist, 1990).

Turner syndrome is the most common chromosomal abnormality that occurs in females. It affects an estimated 3% of all females conceived, but only 1% of these survive to complete a full-term gestation. There are between 50,000 and 75,000 girls and women with Turner syndrome in the United States (Saenger, 1996).

Turner syndrome is highly lethal in embryonic and fetal life. Although 1% to 2% of all conceptuses have 45, X, 98% to 99% of affected fetuses miscarry. When spontaneous abortuses are karyotyped, approximately 10% of them are shown to have Turner syndrome (Hall et al., 1982).